Metabolism Flashcards
Where do molecules come from?
diet, symbiotic organisms, biosynthesis (from scratch), and metabolism!!
what is metabolism
the sum of all biosynthetic (anabolic) and degradative (catabolic) processes
Metabolic pathways
Generation of energy equivalents:
– ATP, GTP, NADH, NADPH
• Consumption of ATP needed for a lot of cell stuff (division, response, gradients, etc.)
Overview of Energy Metabolism
• Compartmentalization of events within cell
– Uptake from extracellular space
– Glycolysis in cytosol
– TCA Cycle and Oxidative Phosphorylation in mitochondria
• Multiplicity of substrates
– Ability to recover energy equivalents (ATP) by oxidation of sugars, fatty acids, and amino acids
Energy Recovery:
Glycolysis
• Linked series of cytosolic enzymes whose activity is subject to control by organism’s energy status and external signals
• Converts 1 unit glucose to 2 units of pyruvate
• Net gain of
– 2 ATP
– 2 NADH (converted to ATP by mitochondrial oxidative phosphorylation)
Energy Recovery: Krebs Cycle
• In mitochondria
• Each 2-carbon unit, entering the cycle as Ac-CoA, yields
– 3 NADH
– 1 GTP
– 1 FADH2
– 2 CO2
• Energy from NADH used for ATP production in oxidative phosphorylation
Energy Recovery: Oxidative Phosphorylation
• Energy derived from oxidation of NADH and FADH2 creates a proton (H+) gradient across inner mitochondrial membrane
• Energy from decay of the H+ gradient used to drive phosphorylation of ADP to form ATP (26 per glucose)
How is this energy used?
• To drive energy-requiring metabolic processes
– interconversion of needed cellular components (monomers and polymers)
– physical movement of molecules, organelles, cells, tissues, limbs…
• To establish and maintain trans-compartmental gradients
– e.g., ionic gradients
• To coordinate and drive the global processes of cell division, survival, differentiation, death
– acute responses to stimuli and accessing information stored in DNA
The metabolism of glucose, amino acids, and fatty acids are regulated by ….
peptide hormones INSULIN and GLUCAGON
released by the pancreas
Insulin
Insulin acts as a fundamental stimulator of glucose and amino acids transport into most types of cells, in support of basic energy metabolism and protein synthesis.
Insulin, when blood glucose levels rise after a meal, also acts to promote the storage of glucose as the polymer glycogen
in the liver and skeletal muscle.
Glucagon
Glucagon, released when blood glucose levels are low, has
the opposite effect on stored glycogen, promoting its breakdown in the liver and the distribution of resulting glucose via the blood circulation.
Insulin release from the beta cells in the pancreatic ‘Islets of Langerhans’ is regulated by….
the sensed levels of glucose in the blood, via a mechanism involving depolarization of the plasma membrane, increased cytosolic Ca2+ concentrations, and the movement of vesicles
containing insulin to the cell surface for release and distribution.
At the surface of its target cells, insulin is recognized by
receptors that are members of the ‘tyrosine kinase’ family of
receptor structures.
Binding of insulin to the receptor activates….
the intrinsic protein kinase activity of the receptor, leading to a cascade of phosphorylation of intracellular proteins that
carry out the cellular responses to insulin (glucose and amino acid uptake, effects on protein synthesis and glycogen and triglyceride storage, etc).
Disorders of energy metabolism involving insulin include …
tumors that chronically secrete insulin in a glucose-insensitive manner, driving blood glucose down to levels insufficient to support energy needs of the central nervous system.
also diabetes
